Kaposi's Sarcoma in the Sigmoid Colon

A 2-week history of diarrhea mixed with bright red blood was the presenting complaint of a 40-year-old man who was seropositive for HIV. Stool studies and culture results were negative for microorganisms. Colonoscopy demonstrated only the raised vascular lesion seen here in the sigmoid colon, which may have been responsible for the bleeding. Biopsy specimens of the lesion showed atypical spindle cell proliferation with destruction of glands, which suggested Kaposi's sarcoma (KS). The patient also had several cutaneous lesions that were identified as KS.

KS usually progresses in an indolent fashion, although it can be aggressive in a small percentage of patients. The lesions generally begin on the feet or ankles and progress proximally. Extracutaneous lesions are most frequently found in the gastrointestinal (GI) tract (most commonly, the small intestine, followed by the stomach, esophagus, and colon). KS in these areas is easily accessible by flexible sigmoidoscopy. In the present case, bleeding was the major complication, but KS can also lead to malabsorption, steatorrhea, and obstruction. Biopsy may fail to recover tumor, however, because of its submucosal location. Surprisingly, biopsy does not cause bleeding; the color of the lesion is attributable to its vascular nature and chronic extravasation of erythrocytes, leading to deposition of hemosiderin.

Chemotherapy can be considered for clinically significant visceral lesions. Local sites causing bleeding in the GI tract have been treated with sclerotherapy, bipolar electrocoagulation, and heater probe.